Q&A with Kit Foster: December 27, 2012

Q. Concerning the Q&A column in the Oct. 25 issue mentioning the 1977 Olds engine, my dad bought a brand-new ’77 Delta Royale off the showroom floor, one of the first to arrive. It was a great car. Later, my neighbor bought a Delta. That was about the time that there were articles about Olds putting Chevy engines in Oldsmobiles. We compared dad’s engine to the neighbor’s, and there were several differences. I believe the batteries, or perhaps the windshield washer containers, were on opposite sides. Dad’s said “Oldsmobile” on the air cleaner, the neighbor’s didn’t. Dad later checked with the dealer service department, and his was indeed made by Oldsmobile. Folks who had the “cheaper” (as they saw it) Chevrolet engine were up in arms. Oldsmobile (I believe) gave them vouchers towards a future purchase, and extended the warranty on the engine. As you said, folks were upset. Later, they just became corporate engines, and the whole thing blew over.

— Dick Bailey Newark, Ohio

A. It wasn’t just batteries and windshield washers that differed. Olds and Chevy 350s had their starters and oil filters “reversed,” too. I hadn’t realized that Buick was implicated in this game of “musical engines,” but apparently so, as Eric Jensen relates below.

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Q. In 1977, my company ordered a 1977 Buick Skylark for my use. We were allowed to select options above the “base fleet car” as long as we paid for them. The plan was to order the 301-cubic inch (5L) V-8, but we were advised that this engine was not certified for California, and the option was the 350 (5.7) with four-barrel carburetor (order code L34). I also added Rallye Ride and Handling and a few other options. When the car arrived the window sticker said: “This vehicle is equipped with a General Motors engine manufactured in a General Motors Plant operated by Chevrolet Motor Division or General Motors of Canada.” The fleet identified the engine as a Chevy. I have a copy of the window sticker if anyone is interested. This car was a bit of a sleeper in the midst of the mostly V-6 Skylarks in the fleet.

— Eric Jensen, San Francisco

A. Thanks for those memories. I recall renting an Apollo, the Nova clone, with Buick’s own 350 in San Diego, circa 1973. That was a pretty spirited car, too.

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Q. I have a 1987 Suburban rear end in my 1985 Chevy pickup, 3.72 gears. I think it is supposed to be a limited slip, but when I power-stand it, only the right wheel burns out. Someone told me that there is a clutch pack in the rear end that must be replaced. How can I check to see if it is a limited slip, and should both wheels spin like a Posi? Is it hard to install this clutch pack?

— Jerry Engel, Sussex, Wis.

A. There are several ways to externally check a differential to see if it is limited slip, but since they don’t all work in the same way, there is no single foolproof method that applies to all cars and trucks. The limited-slip setup on Chevrolet light trucks of the period is described in the service manuals as “a locking rear differential,” and indeed it has multi-disc clutch packs that under light loads “tend to lock axle shafts to the differential case and hence to each other” (this “case” is the housing for the four gears inside the differential, not the outer housing). A “heavyweight governor mechanism” applies the clutches with more force when the wheel-to-wheel speed differs by 100 rpm or more (the difference in normal cornering being less than 100 rpm). However, above 20 mph, the locking feature is disabled, since it is generally not needed for traction in such cases.
The best way to tell for sure if your truck has a limited-slip diff is to remove the cover and look at it. An “open” differential will have the four bevel gears in plain sight, whereas the limited-slip, or “locking” type, will have an outer housing, with the gears visible only through a small hole. The clutch packs are inside this housing.

I have had two Suburbans with locking differentials. One of them had a tendency to momentarily lock up while making slow speed right turns. The dealership advised draining and flushing the case, then refilling with new gear oil and adding the special GM additive needed for this type of differential (using a new gasket, of course). I did so and it helped, but I also needed to repeat the procedure every few years. Replacing the clutch packs seems simple enough in theory — you must remove the axles (there are keepers on the inner ends), and then four bolts should release the entire differential “chuck.” I’ve never done this, however, so I cannot tell you how easily it pulls out, nor how hard renewing the clutches might be.

The above is based on the assumption you have semi-floating axles. Full-floating axles are removed by taking off (usually) eight bolts on the outer hub.

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